This invention relates to the shift control mechanism for an automatic transmission and more particularly to a brake/shift interlock for the shift control mechanism of an automatic transmission in a vehicle such as an automobile or the like.
In vehicles such as automobiles, it is common to employ an automatic transmission. The transmission is capable of being placed in either a Park mode or various non-Park modes by manual actuation of a shift control mechanism. The non-Park modes typically include Reverse, Neutral, Drive, Second and First. The shift control mechanism typically includes a shift lever which is either floor mounted or column mounted on the steering column. Generally, in such shift control mechanisms, there is provided a detent mechanism which interacts with the shift lever to aid in maintaining the lever in a selected position associated with a selected transmission mode.
Recently, a concern has developed regarding a condition termed "sudden acceleration" in which the vehicle may lurch forward or backward when the gear shift lever is moved from Park to one of the non-Park positions such as Reverse or Drive. One technique for minimizing or preventing problem acceleration is to require that the brakes be applied while shifting out of the Park position. While this may normally be good operating practice, it is preferable to provide a interlock which effectively requires that response.
One such brake/shift interlock requires, in addition to the existing shift control mechanism, having a key-actuated interlock cam, or Park/Lock member, (hereinafter P/L member), a further brake interlock cam for blocking the P/L member, a solenoid having a plunger and rigid arm extensible to actuate the brake interlock cam into actuating engagement with the P/L member when the ignition switch is in the Run position and being deactivated when the vehicle's brake is actuated, and a switch for detecting when the shift control mechanism is in the Park position in order to inhibit operation of the solenoid during brake actuation when other than in Park so as to prevent the noise and wear associated with its actuation.
Another such brake/shift interlock is shown in the commonly owned U.S. Patent Application of Ratke et al entitled Brake/Shift Interlock for an Automatic Transmission Shift Control Mechanism, U.S. Pat. Ser. No. 206,255 filed June 13, 1988, which is incorporated herein by reference in its entirety.
It is an object of the present invention to provide an improved brake/shift interlock for preventing undesirable vehicle acceleration when shifting an automatic transmission from the Park position.
Another object of the invention is to provide such a brake/shift interlock which does not generate undesirable actuation noise in operation.
A further object of the invention is to provide a brake/shift interlock having particular utility with column mounted shift control mechanisms. Included in this objective is the provision of an interlock mechanism which is compact and readily mounted to a steering column.
A further object of the invention is to provide such a brake/shift interlock which is cost effective and does not utilize a park position detection switch.
Accordingly, it has been found that the foregoing and related objects are attained in a brake/shift interlock for use with a vehicle transmission shift control mechanism of the type having a column mounted shift lever for selection of transmission modes and a detent mechanism having a detent member and a cooperating insert plate. The detent member is operationally engageable with the insert plate at a plurality of operating positions corresponding to shift lever position (including a park mode position) for retaining the shift lever in selected transmission mode positions. The brake/shift interlock assembly includes a latch for locking the detent member and interconnected shift lever in the park position. The latch is movably mounted for movement between a locking position for locking the detent member in the park position and an unlock position allowing withdrawal of the detent member from the insert plate. An electromagnetic actuator is configured for maintaining the latch in the locking position. The electromagnetic actuator has an actuator rod moveable between first and second positions with the first position being an energized position. The actuator rod is interconnected to the latch so as to position the latch in the locking position when the rod is in the first position. A biasing spring is connected to the actuator rod for normally biasing the rod to the first position to normally bias the latch in the locking position. An electrical control circuit is adapted for interconnection to the ignition switch circuit and brake switch circuit of a vehicle and is configured for selectively energizing the electromagnetic actuator to hold the rod in the first position and thus hold the latch in the locking position when the ignition switch is closed and the brake switch is open. The electromagnetic actuator is de-energized when the ignition switch is open or the brake switch is closed. A spring lever is interconnected to the latch for moving the latch to the unlocked position when the electromagnetic actuator is de-energized and the detent member is being withdrawn from the park position.
The actuator rod is normally biased by the biasing spring so as to normally retain the latch in its locking position. Thus, energizing the electromagnetic actuator does not produce movement of the actuator rod since it is already biased in the locking position. Rather, energizing the electromagnetic actuator serves to magnetically hold the rod in this position and thereby hold the latch in the locking position to lock the detent member and shift lock in the park position. Accordingly, no mechanical movement of the actuator rod or latch is produced by energizing the electromagnetic actuator and no accompanying actuating noise is produced. Further, no actuating noise is generated by brake operation when the transmission is in an operating position other than park.